Capable of sublime artistry and brutal power on a tennis court, sometimes in the space of two strokes, Kyrgios has been tipped as a future grand slam champion from the moment he dismantled Rafael Nadal at Wimbledon in 2014 as a wildcard.

Sadly, it has often been the foul mouth, the stroppy sulks and the occasional bouts of ‘tanking’ that have grabbed most of the headlines -- until this year that is.

Long overdue maybe, but Kyrgios, who former great John McEnroe calls the most talented player of his generation, is beginning to add mental fortitude and reliability to the dizzying array of shots he owns in his arsenal.

The French Open, providing he recovers from a hip problem that has put a major doubt over his participation, is the next test of his ‘greater maturity’, especially as he has managed only five wins in four visits to the claycourt citadel so far.

Two wins already this season over Novak Djokovic and a sensational struggle against Roger Federer in Miami in what was the match of year so far, have certainly given McEnroe, one of Kyrgios’s harshest critics in the past, cause for optimism.

“As a fan of tennis and someone who believes he is the most talented player out there of 21 and under, I‘m very hopeful that he will harness his talent and reach the potential he has,” McEnroe, presenting a popular daily Eurosport show ‘The Commissioner of Tennis’ at this year’s French Open, told Reuters by telephone on Tuesday.

”The good news is that after the Australian Open (defeat) when the question marks came up again he seems to have taken steps in the right direction.

“That match against Roger in Miami was one of the best matches I’ve seen all year. Tremendous. I didn’t anticipate he would have a lot of success on clay but if he is able to play hard all the time, why not? He can win majors.”

There is no question that Kyrgios, ranked 19, has the weaponry needed to win slams with his serve already regarded as one of the best in tennis by none other than Federer.

This season he has won 92 percent of his service games, second only to American John Isner.

As befits a player who could never be described as conventional, his second serve often defies logic.

“He is the master of mysterious when hitting second serves,” Craig O‘Shannessy, the ATP’s strategy analyst, says. “Sometimes it’s an 83 mph kicking mule, other times it’s a 129 mph fastball that whizzes right by you for an ace. It’s unreadable.”

When beating Djokovic in Acapulco, Kyrgios won 75 percent of his second serve points (15/20) against the best returner in tennis -- a statistic that had O‘Shannessy drooling.

“Kyrgios is not simply bending the traditional second-serve rules of our game. He is breaking them in half,” he said.

All that talent counts for nothing though, unless Kyrgios channels his energy in the right direction, which is why his move to hire former French player Sebastian Grosjean as coach was met with such interest from within the game.

”Being unpredictable can be great but you need to train hard and focus,“ former French Open runner-up Henri Leconte told Reuters. ”I think Seb Grosjean will be good for him because he was a worker and knows how to put pressure on his players.

”I doubt Nick has trained once like Seb Grosjean did throughout his career, like six hours a day!

”If Nick starts to train more and start moving better on the clay he could be a monster on this surface.

“He really believes he can be top five in the world. He knows that he can beat the top guys and do something special.”